[Telegram] Add possibility to send photo/image

[goblinmaks]

Could you please add possibility to send/attach photo/image to Telegram message

[amotl]

Dear @goblinmaks,

thank you very much for your suggestion. When reviewing the code base, I find that the pushover, Slack and XBMC plugins already have respective implementations for submitting images.

Maybe I can raise your passion about trying to implement this feature and submitting the patch as a pull request? We would very much appreciate it.

With kind regards,
Andreas.